Rubber powder, ground at ambient temperature, was compounded with polypropylene using only 16 L/D of a co-rotating twin screw extruder. An optimum of extruder configuration and selected process parameters were found for compounds with a rubber filling rate of 50 wt.-%. Restrictions of a reactive compounding were taken into account. The dispersion of the rubber powder is not a limiting process. A compound containing 70 wt.-% rubber powder showed to be overfilled.